update camera in unreal

_posts/UE/2024-10-28 Camera in Unreal.md

@@ -0,0 +1,63 @@
+
+根据 [cameras-in-unreal-engine](https://dev.epicgames.com/documentation/en-us/unreal-engine/cameras-in-unreal-engine) 解释 ViewTarget，`bFindCameraComponentWhenViewTarget`，`bTakeCameraControlWhenPossessed`
+解释 playerController 和 actor 的 `CalcCamera` 函数，`PlayerCameraManager`
+### CameraComponent
+
+### CameraActor
+
+
+`UWorld` 的以下字段记录了游戏中所有的 controller
+```c++
+/** List of all the controllers in the world. */
+TArray<TWeakObjectPtr<class AController> > ControllerList;
+/** List of all the player controllers in the world. */
+TArray<TWeakObjectPtr<class APlayerController> > PlayerControllerList;
+```
+在 `UWorld` 的 tick 函数中，执行完所有 tick group，TimerManager，以及 tickable objects 的 tick 后，会执行所有 player controller 的 `UpdateCameraManager` 函数
+
+player controller 中默认的实现就是调用自己的 player camera manager 的 `UpdateCamera` 函数，player camera manager 的类型由 `PlayerCameraManagerClass` 字段决定，默认是 `APlayerCameraManager`
+```c++
+/** Camera manager associated with this Player Controller. */
+UPROPERTY(BlueprintReadOnly, Category=PlayerController)
+TObjectPtr<APlayerCameraManager> PlayerCameraManager;
+
+/** PlayerCamera class should be set for each game, otherwise Engine.PlayerCameraManager is used */
+UPROPERTY(EditAnywhere, BlueprintReadOnly, Category=PlayerController)
+TSubclassOf<APlayerCameraManager> PlayerCameraManagerClass;
+```
+### PlayerCameraManager
+
+`UpdateCamera` 函数内调用 `DoUpdateCamera` 实际地对 `ViewTarget` 进行更新
+其中调用了 `UpdateViewTarget`，其中有一堆 CameraStyle，默认的情况下调用 `UpdateViewTargetInternal` 函数，BlueprintImplementableEvent 没实现就返回 false
+```c++
+/** Current ViewTarget */
+UPROPERTY(transient)
+struct FTViewTarget ViewTarget;
+```
+### FTViewTarget
+
+`FViewTarget` 的组成
+```c++
+/** Target Actor used to compute POV */
+UPROPERTY(EditAnywhere, BlueprintReadWrite, Category=TViewTarget)
+TObjectPtr<class AActor> Target;
+
+/** Computed point of view */
+UPROPERTY(EditAnywhere, BlueprintReadWrite, Category=TViewTarget)
+struct FMinimalViewInfo POV;
+
+/** PlayerState (used to follow same player through pawn transitions, etc., when spectating) */
+UPROPERTY(EditAnywhere, BlueprintReadWrite, Category=TViewTarget)
+TObjectPtr<class APlayerState> PlayerState;
+```
+
+
+TODO：`UWorld` 的 player controller 从哪来的，我可以继承重载吗
+
+TODO：
+```c++
+/** UPlayer associated with this PlayerController.  Could be a local player or a net connection. */
+UPROPERTY()
+TObjectPtr<UPlayer> Player;
+```
+`UPlayer` 的作用是啥